1. Field of the Invention
The present invention relates to an image forming apparatus of an ink jet system for forming an image by discharging ink from a recording head onto a recording medium.
2. Related Background Art
Up to now, as an output apparatus for a computer or a workstation, there is known an image forming apparatus of an ink jet system for forming an image by discharging ink onto a recording medium such as a recording paper that is transported in a predetermined direction. In general, the image forming apparatus of the ink jet system includes: a recording head provided with plural discharge ports which discharges ink therethrough; a carriage that carries the recording head and scans (reciprocates) in a predetermined main scanning direction; a linear scale for detection of a position of the recording head; and a linear sensor that is fixed to the carriage directly or through a member and reads out graduations formed on the linear scale by moving on the linear scale together with the carriage. The linear sensor is generally arranged in proximity to the recording head, so that the ink discharged from the recording head impacts the recording medium with high accuracy.
When an image is formed on the recording medium by the image forming apparatus of the ink jet system, the recording medium during transportation is temporarily stopped, and the carriage is made to reciprocate in the above-mentioned main scanning direction. At the same time, ink is discharged from ink discharge ports based on signals outputted from the linear sensor having read out the graduations on the linear scale and image signals representing image information. Thus, an image is formed on a portion of the recording medium corresponding to an image forming region that faces the ink discharge ports. After that, the recording medium is transported by a predetermined length and stopped. The carriage is again made to reciprocate in the main scanning direction, while the ink is discharged from the ink discharge ports based on the image signals, and another image is then formed on a different portion of the recording medium corresponding to the image forming region. The above-mentioned operation is repeated to form an image on the recording medium.
In the image forming apparatus of the ink jet system described above, the ink in a liquid state is discharged onto the recording medium to thereby form an image. Therefore, when the ink is discharged from the recording head, ink in a fine mist state (ink mist) occurs around an ink droplet. In addition, when the ink droplet impacts the recording medium, not all the ink mist is adsorbed to the recording medium instantaneously, and there is also a case where a portion of the ink droplet bounces off a surface of the recording medium due to the impact or the like and is scattered in the mist state, thereby generating the ink mist.
The ink mist thus caused is dispersed inside the image forming apparatus along with the scanning by the carriage. The dispersed ink mist adheres to parts or members inside the image forming apparatus. If the ink mist adheres to the linear sensor, there is a fear that the linear sensor erroneously reads out the graduations on the linear scale.
Therefore, there are cases where the linear sensor is arranged apart from the recording head. However, among those cases, there is a case where the accuracy cannot be obtained between the recording head and the linear sensor due to the flexure of a member existing between the recording head and the linear sensor, or the like. As a result, there is a fear that the impact accuracy of the ink discharged from the recording head is reduced. Alternatively, another problem is conceivable in that since the recording head and the linear sensor are arranged apart from each other, the size of the apparatus is increased.